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Neuroradiology Case of the Week

Case 156

Ravinder Sidhu, MD, Loris Cedeno MD, Sven Ekholm MD, PhD,
and PL Westesson MD, DDS, PhD

Clinical Presentation:  A 22-year-old pregnant female with 23 weeks of gestation presented with hydrocephalus on prenatal ultrasound. MR was requested for associated other fetal brain anomalies.

Radiological Findings:  The lateral and third ventricles are dilated with marked thinning of cerebral parenchyma. The atrium of lateral ventricle measures 24 mm (Figs. 1A& B). The fourth ventricle is not dilated. Posterior fossa appears shallow (Fig. 2).

Diagnosis:  Obstructive hydrocephalus, level of obstruction at aqueductal region

Discussion: Ultrasound is the screening modality of choice for fetal imaging. Fetal MR is a correlative imaging modality. It serves as a problem solving tool in cases where ultrasound is able to provide only limited information due to sub-optimal fetal position, maternal obesity and severe oligohydrominios.
      The prenatal diagnosis of hydrocephalus is made exclusively by ultrasound. MR is indicated to look for other associated anomalies as corpus callosum agenesis, cortical dysplasia, heterotopias, masses that might be contributing to hydrocephalus. MR allows a more precise measurement of ventricles. The measurements are best made on coronal images parallel to the brain stem at the level of choroid plexus. Atrial diameter more than 10mm is considered abnormal. As the size of ventricle increases, the prognosis worsens. If atrium is larger than 5 mm, the chance of developmental delay increases to more than 50%. The third ventricle can be measured on coronal and fourth ventricle on sagittal images. The diameter of third ventricle should be less than 4 mm and fourth ventricle should be less than 7 mm.
      Hydrocephalus can be caused by innumerable causes. Aqueductal stenosis can be seen in 20% of patients with hydrocephalus. The narrowing of aqueduct appears to be caused by growth pressures upon the aqueduct from adjacent mesencephalic structures.

References:

1. Levine D, Barnes PD, Robertson RR, Wong G, Mehta TS. Fast MR imaging of fetal central nervous system abnormalities. Radiology. 2003 Oct; 229(1):51-61. [Medline]
2. Barkovich AJ. Pediatric Neuroimaging, 4th Ed. Lippincott Williams & Wilkins 2004, Chapter 8; pgs. 661-669.